Amino Acids (Food Science): Amino and carboxylic acid functional groups can both be found in organic compounds known as amino acids. Although there are more than 500 amino acids in nature, the alpha-amino acids, which make up proteins, are by far the most significant. The genetic code of every living thing contains just 22 alpha glucosamine.
Alpha, beta, gamma, and delta glucosamine can be categorized according to where the main structural functional groups are located; other classifications are based on polarity, ionization, and the type of side chain group (aliphatic, acyclic, aromatic, containing hydroxyl or Sulphur, etc.). glucosamine residues are the second-largest component of human muscles and other tissues, behind water, in the form of proteins. Aside from serving as protein residues,glucosamine also take involvement in the transfer of neurotransmitters and biosynthesis. They are believed to have been crucial in permitting the origin of life on Earth. The Joint Commission on Biochemical Nomenclature of the IUPAC and IUBMB officially names amino acids using the fake “neutral” structure seen in the figure. For instance, alanine is known scientifically as 2-aminopropanoic acid, which is derived from the formula CH3CH(NH2)COOH. Following is how the Commission defended this strategy:
The systematic names and formulae are for hypothetical forms with unprotonated amino groups and undissociated carboxyl groups. This approach is helpful in avoiding a number of nomenclatural issues, but it should not be interpreted as meaning that these structures account for a sizable portion of amino acid molecules.
History
In the early 1800s, the first few glucosamine were identified. The first glucosamine was found in 1806, when French scientists Louis-Nicolas Vauquelinite and Pierre Jean Sobriquet extracted a substance from asparagus that they later termed asparagine. Cystine was found in 18, while cysteine, its monomer, wasn’t found until 1884. Leucine and glycine were found in 1820 . William Cumming Rose, who also identified the necessary glucosamine and defined the minimal daily needs of all amino acids for healthy growth, made the final discovery of the 20 common amino acids in 1935: threonine.
Wirtz acknowledged the unity of the chemical category in 1865, although he did not give it a specific name. The phrase “glucosamine” was first used in the English language in 1898, but the German name, Amino sure, was first used earlier. After enzymatic digestion or acid hydrolysis, glucosamine have been identified to come from proteins. Emil Fischer and Franz Hofmeister separately postulated in 1902 that proteins are made up of a large number of glucosamines, and that these interactions between one amino acid’s amino group and another’s carboxyl group result in a linear structure that Fischer dubbed “peptides.”
General structure of glucosamine
R denotes a side chain unique to each amino acid in the structure at the top of the page. The -carbon is the carbon atom adjacent to the carboxyl group. The word “amino acid” describes amino acids that have an amino group directly connected to the -carbon. These include the secondary amines proline and hydroxyproline. They were previously frequently referred to as amino acids, which is incorrect because they lack the imine grouping HN=C.
Isomerism amino acids
Amino acids often exist in their zwitterionic natural forms, having the molecular formula NH + 3.
The functional groups (NH + 2 in the case of proline) and (CO 2 in the case of glycine) are joined to the same C atom, making them -amino acids. Natural amino acids are the only ones to have the L configuration and are exclusively present in proteins during translation in the ribosome, with the exception of achiral glycine. Since D-glyceraldehyde is dextrorotatory and L-glyceraldehyde is levorotatory, the L and D convention for amino acid configuration refers to the optical activity of the isomer of glyceraldehyde rather than the optical activity of the amino acid itself.
The (S) and (R) designators can be used as an alternate convention to describe the absolute configuration. Almost all (S) amino acids, with the exception of cysteine (R) and glycine (non-chiral), are found in proteins. The side chain of cysteine is located geometrically in the same place as the side chains of the other amino acids, but the R/S terminology is reversed due to sulfur’s higher atomic number than the carboxyl oxygen, which gives the side chain a higher priority by the Cahn-Ingold-Prelog sequence rules. This is in contrast to most other side chains, which have lower priority compared to the carboxyl group due to their atom composition. Rarely, proteins include D-amino acid residues, which are created as a post-translational modification from l-amino acids.
Side chains of Amino Acids (Food Science)
When the amino nitrogen atom is joined to the -carbon, the carbon atom next to the carboxylate group, amino acids are referred to as -. Although there are many methods to categories amino acids, they are frequently categorized according to the polarity of their side chains, as shown in the figure:
Charged side chains amino acids
At a pH of 7, five amino acids have a charge. To enable proteins to dissolve in water, these side chains frequently occur at their surfaces. Side chains with opposing charges then establish crucial electrostatic connections known as salt bridges, which keep structures within a single protein or between interacting proteins stable. In order to selectively attach metal into their structures, many proteins interact with it through charged side chains like aspartate, glutamate, and histidine. Aspartate (Asp, D) and glutamate (Glue, E) are the two amino acids with negative charges when the pH is neutral. In most cases, the anionic carboxylate groups act as Bronsted bases. The aspartic protease pepsin found in the stomachs of mammals may feature catalytic aspartate or glutamate residues that function as Bronsted acids in very low pH settings.
The side chains of three amino acids—arginine (Argo, R), lysine (Lys, K), and histidine (His, H)—are cations at neutral ph. At pH 7, arginine and lysine, which each include charged guanidine groups and charged alkyl amino groups, are entirely protonated. At neutral pH, only around 10% of the imidazole group of histidine is protonated, according to its pike value of 6.0. Histidine frequently takes part in catalytic proton transfers in enzyme processes because it is readily available in both its basic and conjugate acid forms.
Polar uncharged side chains
Serine (Ser, S), threonine (Thru, T), asparagine (Assn, N), and glutamine (Glenn, Q) are polar, uncharged amino acids that easily form hydrogen bonds with water and other amino acids. Normal circumstances prevent them from ionizing, with the catalytic serine in serine proteases being a notable exception. This is not typical of serine residues in general and is an illustration of extreme disruption. In addition to the L (2S) chiral center at the -carbon that is shared by all amino acids with the exception of achiral glycine, threonine also possesses a 3R chiral center at the -carbon. The complete stereochemical formula for threonine is (2S,3R).
Hydrophobic side chains
The mechanisms that fold proteins into their useful three-dimensional structures are mostly driven by nonpolar amino acid interactions. With the exception of tyrosine (Tyr, Y), none of the side chains of these amino acids are easily ionized and do not, therefore, have pikes. At high pH, the tyrosine hydroxyl can deprotonate to generate the negatively charged phenolate. Tyrosine might be classified as a polar, uncharged amino acid because of this, although its extremely low water solubility more closely resembles that of hydrophobic amino acids.
Special case side chains
The charged, polar, and hydrophobic categories do not adequately characterize a number of side chains. Due to its tiny size and the fact that its solubility is mostly governed by the amino and carboxylate groups, glycine (Glee, G) may be regarded as a polar amino acid. Glycine, however, has a special flexibility among amino acids with significant implications for protein folding since it lacks any side chains. Although cysteine (Cays, C) frequently forms covalent interactions with other cysteines in protein structures known as disulphide bonds, it can also readily create hydrogen bonds, which would classify it as a polar amino acid. These bonds are crucial for the development of antibodies and have an impact on the stability and folding of proteins.
Although proline (Pro, P), which has an alkyl side chain and may be regarded as hydrophobic, becomes extremely rigid when integrated into proteins because the side chain connects back onto the alpha amino group. This has a unique effect on protein structure among amino acids, much like glycine. Rare amino acid selenocysteine (Sec, U) is integrated into proteins via the ribosome rather than being directly encoded by DNA. Selenocysteine participates in a number of distinctive enzymatic processes and has a lower redox potential than the related cysteine. Another amino acid, pyrrolidine (Pyle, O), is not encoded in DNA but is instead produced by ribosomes into protein. It is present in archaeal species and participates in a number of methyltransferases’ catalytic activity.
β- and γ-amino acids
NH + 3 CXYCXYCO 2 amino acids, such as -alanine, a component of carnosine and a few other peptides, are known as -amino acids. NH + 3 CXYCXYCXYCXYCO 2 is the structure of -amino acids, and so on, where X and Y are two substituents (of which one is often H).
Zwitterions Amino Acids (Food Science)
Amino acids exist as zwitterions, or dipolar ions, in aqueous solution at pH levels near to neutrality.
NH + 3 CHR CO 2 makes up the main structure, as do CO 2 in charged states. The so-called “neutral forms” NH2, CHR, and CO2H are not present in any appreciable quantity at physiological ph. Although the two charges in the zwitterion structure sum to zero, it is inaccurate to refer to a species as “uncharged” when its net charge is zero. The carboxylate group becomes protonated in severely acidic circumstances (pH below 3), and the structure changes to an ammonoid carboxylic acid, NH + 3 CHRCO2H. However, it does not notably apply to enzymes like pepsin that are active in acidic environments like the human stomach and lysosomes.
Although there are several definitions of acids and bases used in chemistry, only Bronsted’s definition is applicable to chemistry in aqueous solution: A base is a species that can take a proton, whereas an acid is a species that can donate a proton to another species. The groupings in the graphic above are identified using this criterion. The main Bronsted bases in proteins are the carboxylate side chains of aspartate and glutamate residues. Similar to cysteine, lysine, and tyrosine, these amino acids frequently serve as Branstad acids. In these circumstances, histidine can function as both a Bronsted acid and a base.
Isoelectric point of amino acids
The zwitterion predominates for amino acids with uncharged side chains at pH levels in the middle of the two pike ranges, although it coexists in equilibrium with trace quantities of net negative and net positive ions. The balance between the trace amounts of net negative and net positive ions occurs at the halfway point between the two pike values, resulting in a zero average net charge for all forms that are present. The isoelectric point (phi) of this pH is equal to 1 / 2 (pKa1 + pKa2).
The side chain’s pike plays a role for amino acids with charged side chains. Therefore, the terminal amino group for aspartate or glutamate with negative side chains is almost fully in the charged form NH + 3. but this positive charge has to be countered by the negatively charged state that has only one C-terminal carboxylate group. Between the two carboxylate pike values, something happens in the middle: In the equation phi = 1 / 2 (pKa1 + pike(R)), pike(R) denotes the side chain pike.
Other amino acids with ionizable side chains must also be taken into account, such as glutamate (which functions similarly to aspartate), as well as amino acids with positive side chains including cysteine, histidine, lysine, tyrosine, and arginine. Amino acids exhibit zero mobility in electrophoresis at their isoelectric point, while peptides and proteins are more frequently used than single amino acids to take advantage of this feature. Zwitterions have a minimal solubility at their isoelectric point, and by changing the pH to the necessary isoelectric point, certain amino acids (especially those with nonpolar side chains) may be precipitated out of water and separated.
Physicochemical properties
The 20 canonical amino acids can be divided into groups based on how they behave. Charge, hydrophilicity or hydrophobicity, size, and functional groups are significant variables. Protein structure and protein-protein interactions are influenced by these characteristics. Leu, Ile, Val, Phi, and Tarp are hydrophobic residues that are frequently buried in the center of water-soluble proteins, whereas hydrophilic side chains are exposed to the aqueous solvent. An individual monomer found in the polymeric chain of a polysaccharide, protein, or nucleic acid is referred to as a residue in biochemistry. The outer rings of exposed hydrophobic amino acids on the integral membrane proteins usually serve as anchors for the proteins in the lipid bilayer. A patch of hydrophobic amino acids on the surface of several peripheral membrane proteins causes them to adhere to the membrane.
Certain amino acids have unique qualities. Other cysteine residues and cysteine can bind covalently through disulfide bonds. Glycine is more flexible than other amino acids, and proline creates a cycle to the polypeptide backbone. Unlike the other amino acids, which are highly reactive, complex, or hydrophobic, such as cysteine, phenylalanine, tryptophan, methionine, valine, leucine, and isoleucine, glycine and proline are substantially more prevalent in low complexity regions of both eukaryotic and prokaryotic proteins. Numerous proteins go through a variety of posttranslational modifications, in which extra chemical groups are sometimes attached to the side chains of amino acid residues to produce lipoproteins, which are hydrophobic, or glycoproteins, which are hydrophilic, enabling the protein to momentarily bind to a membrane. For instance, a signaling protein may adhere to a cell and then separate from it.
Occurrence and functions in biochemistry
Since they help make proteins, amino acids with the amine group linked to the (alpha-) carbon atom adjacent to the carboxyl group are of particular relevance to living things. They are referred to as 2-, alpha-, or -amino acids (most commonly having the general formula H2NCHRCOOH,[c] where R is an organic substituent known as a “side chain”); frequently, the word “amino acid” is used to explicitly refer to them. They contain the 22 proteinogenic amino acids (also known as “protein-building”), which are combined to produce peptide chains (also known as “polypeptides”), which are the fundamental units of a wide variety of proteins. All of these are L-stereoisomers, or “left-handed” enantiomers, with the exception of a few D-amino acids, or “right-handed” enantiomers, which can be found in certain antibiotics, bacterial envelopes, and D-serine, a neuromodulator.
Numerous glucosamine, both proteinogenic and non-proteinogenic, have biological use. For instance, the principal excitatory and inhibitory neurotransmitters in the human brain are glutamate (standard glutamic acid) and gamma-aminobutyric acid (nonstandard gamma-amino acid, or GABA). Proline is converted into hydroxyproline, which is a crucial part of the collagen found in connective tissue. Red blood cell-useable porphyrins are biosynthesized from glycine. Using carnitine helps move lipids. Because the human body is unable to synthesize nine proteinogenic glucosamine from other substances, they must be consumed through diet. These glucosamine are referred to as “essential” for humans. For particular ages or medical circumstances, others can be deemed conditionally necessary. Species-to-species variations in essential glucosamine are also possible. Amino acids are vital in biological processes because of their biological relevance.
Proteinogenic amino acids
Proteins are built from amino acids. They combine through condensation processes to create either shorter polymer chains termed peptides or proteins, or longer chains known as polypeptides. These chains are linear and unbranched because each amino acid residue is joined to two neighboring amino acids.The process of creating proteins in nature that are encoded by DNA/RNA is known as translation, and it entails a ribozyme called a ribosome adding amino acids one at a time to a building protein chain. An mRNA template, which is an RNA copy of one of the organism’s genes, is used to read the genetic code and determine the sequence in which the amino acids are added.
Proteinogenic or natural glucosamine are the 22 amino acids that are naturally integrated into polypeptides. Twenty of them are encoded by the whole genetic code. Selenocysteine and pyrrolidine, the remaining 2, are integrated into proteins using certain synthetic methods. When an SECIS element is present in the mRNA being translated, the UGA codon inserts selenocysteine rather than a stop codon.Some methanogenic archaea employ pyrrolidine in the enzymes they use to generate methane. It is represented by the codon UAG, which in other species is often a stop codon. Immediately after this UAG codon, a PYLIS downstream sequence follows.
Glee, Ala, Asp, Val, Ser, Pro, Glut, Leu, and Thru may be related, according to several independent evolutionary analyses.
Reference
- https://medlineplus.gov/ency/article/002222.htm#:~:text=Amino%20acids%20are%20molecules%20that,the%20building%20blocks%20of%20life.
- https://en.wikipedia.org/wiki/Amino_acid
- https://my.clevelandclinic.org/health/articles/22243-amino-acids
